Detection of terahertz radiation by AlGaN/GaN field-effect transistors

High electron mobility transistors can work as room-temperature direct detectors of radiation at frequency much higher than their cutoff frequency. One open issue is how the radiation couples to the sub-wavelength transistor channel. Here, we studied the coupling of radiation to an AlGaN/GaN transistor with cut-off frequency of 30 GHz. Local irradiation with a free electron laser source at 0.15 THz allowed us to selectively couple the signal to the channel through one transistor terminal at a time. Far-field experiments at 0.15-0.94 THz were also performed in order to study the nonlinear properties of the transistor channel.